1. Field of the Invention
The present invention relates generally to a packet-switched network. More particularly, the present invention relates to a method and apparatus for performing Layer 3 (L3) handover between Core Network (CN) entities in a packet-switched network.
2. Description of the Related Art
The Universal Mobile Telecommunication System (UMTS), an asynchronous 3rd Generation (3G) mobile communication system based on European Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS) and operating in Wideband Code Division Multiple Access (WCDMA), provides a uniform service of sending packet text, digital voice or video, and multimedia data at or above 2 Mbps to mobile users or computer users irrespective of their locations. With an introduction of a concept of virtual access, UMTS enables access to any end point within a network. The virtual access refers to packet-switched connection using a packet protocol like Internet Protocol (IP).
Compared to the UMTS system where network entities are connected in Asynchronous Transfer Mode (ATM) and connected to an external packet data network via a gateway node (that is, Gateway GPRS Support Node (GGSN)), Enhanced-UMTS (E-UMTS) offers IP-based connectivity between network entities, thereby reducing the number of intermediate nodes via which a User Equipment (UE) is connected to the packet data network and thus enables fast data transmission.
A typical UMTS system is comprised of radio access networks (RANs) and a CN. A radio access network (RAN) takes charge of Layer 1 (L1) and Layer 2 (L2) protocols and is wirelessly connected to UEs. The CN takes charge of a L3 protocol and connects the RAN to an external network. The UMTS system provides L2 handover through Serving Radio Network System (SRNS) re-allocation and L3 handover through inter-Serving GPRS Support Node (inter-SGSN) handover.
As the typical UMTS system has evolved toward the packet switching-based 3G mobile communication network, there is a need for supporting fast and seamless handover between RANs belonging to different CN entities.